This invention relates to a variable wall mining machine to not only release coal from the face of a longwall mine, but also to transport the coal released from the mine face without the need for auxiliary conveying equipment at the longwall mine face. More particularly, the present invention relates to such a variable wall mining machine including side-cutting auger sections joined together in an end-to-end relation by universal joints for sumping movements in pairs in a progressive manner commencing from one end of the auger assembly to the other end and followed thereafter by movements of the auger sections in pairs for shear cutting the mine face in the same progressive displacement manner as provided for sumping cuts.
As is known in the art, a cutting device, such as a scroll or auger with bits mounted thereon, is a feasible device for releasing coal from a longwall mine face. The scroll or auger is rotated so that the bits dig into the coal face to release the coal therefrom. At the same time, the scroll or auger provides a mechanism by which the coal may be transported away from the site of the mine face. Such a device, for example, is shown in U.S. Pat. Nos. 3,524,680 and 3,640,580. The mining machine disclosed in these patents includes the use of a plurality of axially-aligned augers which are connected together by a sleeve and driven from opposite ends. The helical edges of the auger are provided with hardened cutting points to release coal from the coal vein. Pressure is applied to the augers laterally thereof at spaced points to gradually move the entire string of augers as a whole into the vein of coal and effect cutting thereof. A scavenger board is carried at the side of the augers opposite the vein of coal. A device of this type for releasing coal from a mine face differs from the conventional auger-type miner in that the cutting is effected at the circumference of the auger rather than head-on. Transportation of the coal released during the mining operation is carried out by the auger as in conventional auger-type mining. In this type of auger mining machine, the string of augers is fed into an exposed highwall of a coal face for a distance up to, for example, 200 feet and, in some cases, even 300 feet and provides very high productivity. However, a mining machine of this type is inefficient in terms of kilowatt hours per ton of coal released from the mine face in light of the depth of penetration per bit. Generally, the linear speed of the cutting bits was high but the penetration per bit was low. The speed at which an auger having a given design can be rotated is a function of the rate at which coal is released from the mine face and the rate at which the released coal can be transported by the auger. Increasing the speed of the auger enables a more rapid transportation of the coal; however the higher linear speed of the bit across the coal face brings about a demand for increased horsepower with little increase in production. Tests have shown that increasing the auger speed of rotation by 20 revolutions per minute, for example, will yield about the same coal output per kilowatt hour while significantly decreasing the service life of the cutting bits.
The use of an auger with cutting bits on the side edge thereof provides a highly desirable form of mining machine; however the known arrangement of parts to effect the release of coal has certain acute disadvantages which the present invention is designed to overcome. Specifically, for example, when the auger which may have a string length of as much as 500 feet is moved into contact with the mine face along the entire length thereof, the power requirements become excessively large. The need to uniformly advance the auger along its entire length into the mine face cannot be accomplished within acceptable limits, thus damaging forces are imposed on the torque-transmitting shaft component of the auger causing the joints between the auger segments to break as well as the auger shaft itself. Increasing the shaft size to meet the torque requirements significantly reduces the conveying capacity of the auger itself, and thus is not an acceptable solution. Also the physical size of a motor to drive a full sumping machine could not be brought into a mine let alone suitably housed in a mine section. Moreover, the power supply to the motor would be difficult to install and maintain.